Old school thinking suggested vitamin D3 toxicity at under 10,000 without any evidence.
Recently better info has been gained and 70,000 IU may show signs of toxity or repeated exposure to 40,000+IU. As a night shift worker i supplement daily with between 8-16,000 IU, from a very concentrated powder that is hard to measure accurately.

I'm on 20,000 IU a day. Its easy to get deficient in the North of England. A friend of mine is a doctor specialising in vit D research. He usually prescribes as a minimum 10,000 IUs a day for 3 months for someone who is deficient.

Vitamin D: The Sunshine Vitamin
You need vitamin D for healthy bones and to boost your immune system, but use care when getting it from sun exposure. Eating fortified foods and taking dietary supplements are safer.
By Beth W. Orenstein
Medically reviewed by Lindsey Marcellin, MD, MPH
Print Email
Vitamin D, an essential vitamin, is both a hormone-like compound and a fat-soluble vitamin, says Roberta Anding, MS, RD, sports dietitian at Memorial Hermann Sports Medicine Institute in Houston and a spokesperson for the American Dietetic Association. “Almost all cells and tissues of the body require vitamin D.”

Vitamin D is naturally present in very few foods. However, vitamin D is often added to other foods, sometimes called vitamin D-fortified foods, and can also be taken as a dietary supplement. Also, when the skin is exposed to the sun, our bodies make vitamin D. “That’s why it’s often referred to as the sunshine vitamin,” Anding explains.

Vitamin D's benefits include:

It brings calcium to your bones and teeth, helping to protect you against bone diseases such as osteoporosis. Its role in bone health is probably the best-known vitamin D benefit, Anding says.
It regulates how much calcium stays in your blood, contributing to heart health.
It helps strengthen your immune system and regulate cell growth.
Good Vitamin D Sources

Milk
Breakfast cereals
Margarine
Orange juice
Yogurt
Cheese
Bread
Soy drinks
There's more content below this advertisement. Jump to the content.
Read the nutrition facts panel of the product to see if it has been fortified with vitamin D.

Most people can produce adequate amounts of vitamin D by getting 10 to 15 minutes of sun exposure every day. But using sunscreen can block vitamin D production, and individual sun exposure needs depend on your complexion, whether you live in a northern latitude, and seasonal factors.

Anding says risking a sunburn isn’t a good way to get your dose of vitamin D. Indeed, the American Academy of Dermatology recommends against getting vitamin D from sun exposure or tanning salons and instead suggests relying on dietary supplements.

“Dietary supplements of vitamin D are safe and effective,” Anding says. “They can be useful since food sources are limited, and it can be problematic if you don’t like the few food sources there are.” Vitamin D comes in two major forms, D2 and D3. D3 is most effective, but D2 is a vegetarian’s best choice, Anding says.

Getting the Right Amount of Vitamin D

The older you are, the more vitamin D you need. The current recommended daily dose of vitamin D is 200 IU (international units) for people up to age 50, 400 IU for people age 51 to 70, and 600 IU for people over age 70. The American Academy of Pediatrics recommends that infants receive 400 IUs of vitamin D daily for as long as they are breastfed, since breast milk is not a source of vitamin D. Infant formula is fortified, and babies who consume 27 to 32 ounces a day do not need additional vitamin D. Studies show a lack of vitamin D early in life increases one’s risk of multiple sclerosis, Anding says.

At the same time, large amounts of vitamin D are considered toxic. People who get too much vitamin D may feel nauseated, constipated, confused, or have abnormal heart rhythms and even kidney stones.

“The current upper limit is 2000 IU per day,” Anding says. “However, many vitamin D experts are challenging the validity of this upper limit.” Since measuring vitamin D levels has become more common in doctors' offices, many people have been found to have inadequate blood levels. These people are often treated with daily or weekly supplements in much larger doses.

Is There Even More Value in Vitamin D?

Vitamin D has been all over the news in recent years, with many claims being made about its powers to improve health. Several studies have suggested that vitamin D can improve one’s ability to fight cancer, including breast cancer.

There are also suggestions that vitamin D can prevent a wide variety of illnesses and some evidence that taking vitamin D supplements can decrease risk of getting seasonal influenza A in children, as well as decrease the risk of asthma attacks.

You need vitamin D to keep your bones healthy and protect against osteoporosis. Most people get adequate amounts of vitamin D from limited exposure to the sun and through diet, but people who are inside all day and who don’t like any of the foods that are good sources of vitamin D or that have been fortified with vitamin D, such as milk, should consider taking dietary supplements. Consult your doctor for an individualized recommendation for how much is right for you.